PARASITISM

IT IS THE RELATIOSHIP BETWEEN TWO INDIVIDUALS OF DIFFERENT SPECIES IN WHICH THE PARASITE RECEIVES BENEFIT AT THE EXPENSE OF THE HOST; THEREFORE , PARASITISM IS A FORM OF THIS OPERATION. IN THIS  ASSOCIATION, THE PARASITE RECEIVES FOOD, SHELTER AND PROTECTION AT THE EXPENSE OF THE HOST.

THE ORIGIN OF A PARASITIC LIFE IN AN ANIMAL IS ASSOCIATED WITH ATTEMPTS TO SECURE FOOD FOR THEMSELVES OR THEIR OFFSPRING. THE ANCESTORS OF ECTOPARASITES  WERE CLEARLY FREE LIVING FORMS. A FREE LIVING ORGANISM COULD HAVE ACCIDENTALY SETTLED ON THE BODY OF A LARGER SPECIES WHERE CONDITIONS WERE MORE FAVOURABLE FOR SURVIVAL. THERE ARE CERTAIN MODIFICATIONS AND ADAPTATIONS WHICH MIGHT HAVE EVOLVED  IN THESE ORGANISMS.

ORGANS OF ATTACHMENTS: THE TAPEWORM HAS HOOKS FOR ATTACHMENT TO THE HOST'S GUT WALL.


BODY SHAPE: THE INTESTINAL PARASITES LIKE THE ROUND WORM HAS AN ELONGATED BODY.


CUTICLES: THE INTESTINAL PARASITES LIKE THE  TAPEWORM HAVE THICK CUTICLES WHICH OFFER THEM  RESISTANCE AGAINST THE ACTION OF THE DIGESTIVE JUICES.


LOSS OF LOCOMOTARY ORGANS: MOST ENDOPARASITES LIKE FLEAS (THEY HAVE LOST THEIR WINGS, HAVE LOST THEIR LOCOMOTIVE ORGANS AS THEY ARE NOT NEEDED. THESE ORGANS MAY DISAPPEAR OR DIFFERENTIATE  INTO ORGANS OF ATTACHMENTS.


LOSS OF SENSE ORGANS: AS THE INTERNAL ENVIRONMENT OF THE HOST  IS MORE OR LESS UNIFORM, THERE IS NO USE OF SENSE ORGANS AMONG ENDOPARASITES AS THEY ARE  PROVIDED ONLY WITH TANGO RECEPTORS.


DIGESTIVE SYSTEM: THE TAPEWORM HAS LOST ITS DIGESTIVE SYSTEM, ITS MOUTH PARTS  HAVE DEVELOPED PIERCING AND SUCKING APPARATUS TO CONSUME THE ALREADY DIGESTED FOOD.


COMPLICATED REPRODUCTION : THE ROUNDWORM IN HUMANS LAYS EGGS AT THE RATE OF 1500 A DAY, THE TERMATODES LAY EGGS CONTINUOUSLY, AND THE TAPEWORM LAYS EGGS ANNUALLY, ESTIMATED AT 80 MILLION PER YEAR.

THE EFFECT OF PARASITISM ON THE HOST IS USUALLY HARMFUL. THE EFFECT OF PARASITISM ON THE HOST IS USUALLY HARMFUL. THE EFFECTS OF ENDOPARASITES ARE MORE MARKED THAN THOSE ECTOPARASITES.